The present invention relates to an electron multiplier element of the "apertured plate" type with secondary emission. The invention also relates to an electron multiplier device comprising a parallel stacking with N electron multiplier elements of secondary emission according to the invention and an application of said multiplier device to a photomultiplier tube.
An electron multiplier device as described in the opening paragraph is known, for example, from French Patent Specification No. 2,299,722. This Specification describes an electron multiplier tube which consists of a stack of electron multiplier elements with secondary emission, each formed by two apertured demi-plates having concave walls, the assembly being such that when the demi-plates are combined the corresponding holes of each demi-plate form a single barrel-shaped hole. The walls of said holes are coated with a layer of material with secondary emission in which the useful part of each single hole is formed by the lower half-hole. The advantage of such a structure of electron multiplier elements is that it enables the multiplication, with little space, of the incident electrons presenting themselves at the level of the plate in the form of a wide beam, for example a cylindrical beam, without it being necessary to use an electron focalization optical system. On the other hand, a recurring structure of small pitch is well suitable to form intensified pictures.
However, the disadvantage of this type of electron multiplier elements is that a significant number of incident electrons does not cause secondary emission because some of them directly traverse the multiplier holes without being subjected to multiplication while others reach the multiplier elements in places where the secondary electrons cannot be extracted, for example between two holes or beyond the effective part of the holes.